Recently, as the world entered the information age, display devices for processing and displaying a large amount of information have been rapidly developed. Accordingly, various display devices have been developed and have attracted a lot of attention.
Specific examples of the display devices may include a liquid crystal display device (LCD), a plasma display panel device (PDP), a field emission display device (FED), an electroluminescence display device (ELD), and organic light emitting diodes (OLED). These display devices generally have excellent properties of a thin profile, light weight and low power consumption and thus their application fields have been increased continuously. In particular, in most of electronic devices or mobile devices, the display device has been used as one of a user interface.
Also, studies of transparent display devices through which a user may see objects or images located on the opposite side are being actively conducted.
The transparent display devices may have advantages of better use of space, interior and design, and may have various application fields. The transparent display devices may solve spatial and temporal restrictions of electronic devices as compared with conventional display devices by implementing a display device with functions of information recognition, information processing and information display as a transparent electronic device. Such transparent display devices may be used for a smart window, which may be used as a window of a smart home or a smart car.
Particularly, an LCD may be implemented as a transparent display device by applying an edge type backlight thereto, but a transparent display device based on LCD has a problem in that a transmittance ratio is very low and transparency is decreased by a polarizing plate used for implementation of black and also has a problem with outdoor visibility.
Further, a transparent display device based on OLED has higher power consumption than the transparent display device based on LCD and has difficulty in displaying a true black. Also, the transparent display device based on OLED has no problem with a contrast ratio under a dark environment, but has a disadvantage of reduction in a contrast ratio in a normal environment with light.
Therefore, in order to implement a transparent mode and a light shielding mode, there has been suggested a method for utilizing a polymer dispersed liquid crystal (PDLC) and a polymer networked liquid crystal (PNLC) for a light control device of the transparent display device based on OLED. The polymer dispersed liquid crystal (PDLC) or the polymer networked liquid crystal (PNLC) may be formed by mixing a monomer with a liquid crystal and then irradiating ultraviolet (UV) rays thereto.
Particularly, the polymer dispersed liquid crystal (PDLC) has a structure in which a liquid crystal is formed within a droplet, and the polymer networked liquid crystal (PNLC) has a structure in which a polymer is distributed in a network structure on a liquid crystal.
If an electric field is applied to the polymer dispersed liquid crystal (PDLC) or polymer networked liquid crystal (PNLC), an alignment of the liquid crystal is changed, and, thus, light incident from the outside can be scattered or transmitted. That is, a device using the polymer dispersed liquid crystal (PDLC) or polymer networked liquid crystal (PNLC) can scatter or transmit light without a polarizing plate, and, thus, can be used as a light control device of a transparent display device.